Among the more unpleasant mythemes that one group of humans has devised about another is the blood libel: the claim that Jews murder Christian children, often around Easter, and use their blood in Passover rituals. Bits and pieces of this myth date back to ancient times. The Greek world produced some sinister stories about Jews annually fattening a Greek in their temples for sacrifice. And the New Testament (Acts 7:51–53) and the Quran (2:87) have cast Jews as persecutors and murderers of prophets. But the specific ingredients of the blood libel—innocent children murdered by conspiratorial Jews for blood rituals—were not baked into narrative until a child’s corpse was discovered in 12th century England and an enterprising monk accused the local Jewish community of murder. That first accusation sputtered out, but others soon followed in France and Germany that sometimes resulted in the execution of entire communities. With the invention of the printing press, the myth spread even more widely, throughout Eastern Europe and, with colonialism, into the Middle East and beyond. In the 20th century, there was even a genre of postcards depicting Jews draining the blood from young Christian boys.

Magda Teter’s terrifying and learned new book, Blood Libel: On the Trail of an Antisemitic Myth, examines some of the long history of this pernicious idea. Her focus is firmly on the past and especially on the death in 1473 of one toddler, Simon of Trent. His lifeless body provided the stage for a spectacular trial against the Jews of that town—one whose consequences would be felt for hundreds of years. Teter sets out to document how the information about Simon’s death circulated during and after the trial and how it eventually flowed into Eastern Europe, where the myth put down some of its deepest and cruelest roots. She certainly succeeds in that historical task. While her claims are specific and circumspect, her book can be read more broadly as an allegory for our age, a story about how technological change, religious beliefs, struggles for power, and a politics of demonization can produce memes capable of transmitting the potential for violence across vast amounts of time and space.

In the case of the blood libel, that potential remains very much alive. “You are not forgotten, Simon of Trent,” wrote the 19-year-old gunman who stormed a synagogue near San Diego on the final day of Passover last year. “The horror that you and countless children have endured at the hands of the Jews will never be forgiven.”

Blood Libel’s trail starts almost a millennium ago, in 1144, with the discovery in Norwich, England, of the corpse of a 12-year-old named William. Although some of the local clergy may have accused the Jews at the time, little notice was taken until a few years later, when a monk called Thomas of Monmouth moved to town. He spent the next two decades attempting to establish the dead boy as a martyr killed by Jews and promoting the church where he was buried as a site of pilgrimage. In The Life and Passion of William of Norwich, Thomas developed many of the themes that would become staples of the blood libel genre: the seeming kindness with which Jews seduce an innocent child; the hideous tortures to which they subject him in reenacting Christ’s passion; the ritual nature of the crime, repeated annually; the Jewish community’s “inborn hatred of the Christian name”; the conspiracy by state authorities, bribed by Jewish money, to cover up the crime; and the many miracles by which the Christian truth overpowers the lies of murderous Jews and their corrupt Christian allies.

As far as we know, very few people read Thomas’s manuscript in the Middle Ages. We can’t say with any confidence that it was the origin of the blood libels to come. What we can say is that its basic storyline soon appeared elsewhere in Europe. Perhaps this success was the product of more general trends in Christian piety: With increasing devotion to the cult of the Virgin Mary and the infant Jesus, it became easier to see in every Christian child a figure of the Savior, supposedly hated by Jews. Or perhaps it was animated by the increasing reach of kings and their governments, which sometimes used Jewish moneylenders and tax collectors to extend their power, providing the Christian populace with new reasons to resent the tiny minority living among them.

In short, we really don’t know why this particular story suddenly became so convincing. But we do know that its main themes reemerged in 1171, when the leading Jews in Blois, France, were accused of killing a Christian child and were burned alive for the crime, despite the fact that no child was reported missing and no body was ever found. It then cropped up in 1235, when 34 Jews were executed in Fulda, Germany, after five children burned to death in their home while their parents were at church. Twelve years later, the Jews of Valréas in southern France were tortured and executed after being accused of extracting the blood from a 2-year-old girl named Meilla during Holy Week. Blood Libel recounts all of these early examples. But Teter makes clear that she doesn’t think of the blood libel as particularly medieval. The Middle Ages may have pioneered the accusation of ritual murder, but in her view it was only in the modern era, with new technologies like the printing press and new conflicts between princes and popes, that the libel became a powerful and dangerous myth capable of spreading across Europe.

Teter is right to note that during the Middle Ages these charges were sometimes met with skepticism as well as credulity. In 1247, after the attacks in Fulda and Valréas, Pope Innocent IV issued the papal bull Sicut Judaeis, in which he forbade Christians to accuse Jews of using human blood in their rituals, on pain of excommunication. The pontiff pointed out that “in the Old Testament they are instructed not to use blood of any kind, let alone human blood.” That official medieval skepticism, Teter writes, disappeared with modernity. The Enlightenment Pope Benedict XIV (1740–58) notably condemned slavery and appointed a woman as a professor of the sciences at the University of Bologna. But he was also the first pope to formally approve the cults of Simon of Trent and other child martyrs, effectively annulling Innocent’s teaching and affirming the accusations against Jews. The cult of Simon was not formally abolished by the Catholic Church until the 20th century, with a brief “Notification” published in the diocesan bulletin of Trent in October 1965.

While it is true that medieval monarchs and popes could be quite skeptical of the blood libel, it was likely more widespread in the Middle Ages than Teter allows. Even in regions where there were few full-blown ritual murder trials, like Spain, there may have been widespread awareness of the charge. Alfonso de Espina, the confessor to the king of Castile and one of the most influential Castilian clerics, was loudly urging prosecutions for blood libel over a decade before Trent. And though he doesn’t seem to have succeeded in staging a trial, he did play a very important role in disseminating the accusation. In 1458 he penned a massive tome, The Fortress of Faith, dedicated to proclaiming the crimes of Jews, Muslims, and heretics against Christianity, including a history of the ritual murders allegedly committed by Jews. The treatise was among the very first books to be produced on the newly invented printing press in Gutenberg’s Germany; it then circulated widely in Europe and became an authoritative reference for those arguing that Jews ritually murder Christians for their blood.

In fact, long before de Espina, stories of ritual murder were sufficiently well known on the Iberian Peninsula for Jewish communities to worry about them. When the Jews of Barcelona found a baby’s corpse in their meat market in 1301, they reached out immediately to the municipal authorities, fearing that violence would follow. The Jews of Trent did the same in 1475, when they found little Simon floating in the canal beneath their homes. In other words, even where we find few records of trials, the libel may have been bubbling beneath the surface, widely available to the late-medieval Christian imagination.

Even so, why did the Barcelona baby disappear into the archival dust while Simon of Trent was thrust onto the historical stage? Although Teter never asks that question, she provides an indirect answer to it: The new technologies and sciences that we associate with the Renaissance, the Enlightenment, and modernity are what made the attack on Trent’s Jews so powerfully meaningful for the future. The printing press, which entered the world not long before Simon was born, was one of those technologies. And history, newly empowered by humanism and the emergence of new reading publics, was one of those sciences.

Among this book’s grimmest pages are those that discuss the “strategic communications” techniques that this new technology enabled Bishop Johannes Hinderbach of Trent to deploy. Simon wandered away from his home on Holy Thursday, March 23, and was found dead on Easter Sunday. By the 31st, the bishop’s notaries were preparing for the press records of miracles allegedly performed by the boy’s corpse. A narrative of the murder by the bishop’s personal physician was quickly published in Latin, German, and Italian accusing Jews of the crime, calling them a “savage race,” and demanding their elimination “from the whole Christian world.” This account was then sent to a poet in the bishop’s circle to be rendered into verse and song, thereby making it easier to remember and declaim, and soon printed in multiple languages for the broadest possible audience.

This media storm succeeded in motivating judicial proceedings against the Jews in Trent and legitimizing their torture. When that torture took place, it isn’t surprising that the interrogators’ script followed the physician’s and poet’s, already widely circulated and read. The pain of torture was extreme and persuasive, so much so that when one of the accused women refused to speak, officials could explain her resistance only as magic. The bishop ordered her to be washed from head to toe with the urine of a virginal boy to counteract the spell—this from a man accusing Jews of using Christian bodily fluids in their rituals!—but to no avail. Apparently, she never confessed. But others were less enduring. “Tell me what you want me to say and I will say it,” pleaded one defendant to his interrogators. Small wonder that some of the resulting confessions follow the initial accusations or that the defendants were all convicted.

The images and arguments created and transmitted by the impresarios of the Trent ritual murder trial, the chapels those impresarios built, and the pilgrimages they promoted and popularized found their way into the Christian imagination. Teter’s book is particularly strong—and original—in following those images, arguments, and pilgrimages as they flowed to and from Eastern Europe, driving accusations, trials, and massacres in the lands we today call Poland, Ukraine, and Lithuania. Some of those stories from Eastern Europe would in turn make their way westward, put to work by the Nazis in their extermination of Jews. Twentieth century Germans could send one another gruesome postcards, like the one urging its recipient to “Remember the 11th of March, 1900,” when the Jews of Konitz were accused of sacrificing a Christian student for Passover. (This example is not in Teter’s book.) Little Simon had a starring role in Der Stürmer’s special ritual murder issue in 1934. Today such murderous messages are seldom delivered on paper, but they are no less accessible for that, as Blood Libel’s first sentence makes clear: “In 2014, the Anti-Defamation League appealed to Facebook to take down a page titled ‘Jewish Ritual Murder.’ It took four years until the page was finally removed.”

New types of media don’t merely disseminate knowledge in new ways; they also generate forms of knowledge. This was as true of the rise of the printing press as it is in our age of social media. And here we come to what has to be, for anyone in my profession, the saddest of this sad book’s lessons: the complicity of history and historians in the transformation of the blood libel from superstition (as Innocent IV might have called it) into scholarship.

As Teter documents, that transformation took place with stunning rapidity. An illustrated Hystorie von Simon zu Trient was published with the bishop’s support in early September 1475. Its images and its narrative were repeated again and again by historians. Among the most influential of these was “the highly learned Doctor Hartmann Schedel,” whose history “from the beginning of the world to our own time” is known today as the Nuremberg Chronicle because it was published in that German city in 1493. (De Espina’s Fortress was published by the same press eight years earlier and was republished by it the following year.)

The Chronicle incorporated the blood libel into its version of world history. Its entry for 1144 is the story of William of Norwich and for 1475 the “Blessed Simon of Trent.” The image illustrating Simon’s story on the reverse of the Chronicle’s folio 254 is perhaps the most famous representation of ritual murder in history. It is worth noting that the image is virtually identical to the one that Hinderbach’s printers produced for the posters they distributed in Trent in 1475. Historians have always been ecologically minded, recycling materials they find in earlier sources. In this instance, they repackaged innovative propaganda into the most up-to-date “scholarship.”

Wherever the blood libel traveled, it was accompanied by historians. This was as true of its dispersal in 17th and 18th century Poland and Lithuania as it was of its diffusion in the 19th and 20th century Islamic world (a subject not covered in this book). On each stage of the journey we find the past marshaled as evidence, either to support the charge of ritual murder or to rebut it.

The Polish priest Stefan Żuchowski, the impresario behind not one but two blood libel accusations in the city of Sandomierz in 1698 and 1710, certainly understood this. In his efforts and in a how-to manual he produced for future accusers, Żuchowski stressed the importance of sifting through history to find examples of Christian blood spilled by Jews in “foreign and [Polish] chronicles.” It was as a reward for his mastery of this vicious science that the synod of Kraków diocese bestowed on him the title of commissary for Jewish affairs in 1711.

Blood Libel is not only about those Christians who put these new technologies to work against Jews. Teter also introduces us to some who used the printing press and the cutting edge of historical scholarship in defense of the accused. In 1669, 3-year-old Didier and his mother were in a forest near Metz, at the border between France and the Duchy of Lorraine, when the boy disappeared. His body was never found, but the rumor of a Jewish kidnapping spread, and soon enough Raphaël Levy, a Jew from Lorraine, was charged with the crime, an accusation that then spread to include the Jews of Metz. Levy, a foreigner without French protectors, was publicly executed in January 1670. Though it came too late to save him, the Jews of Metz managed to secure the intervention of the Parisian scholar and theologian Richard Simon. The brief he produced in 1670 was replete with documentation, from medieval papal bulls to records from a blood libel trial held in Verona in 1603. Its goal was to demonstrate that the historical references favored by Levy’s accusers, drawn from books like the Nuremberg Chronicle and the Annales Ecclesiastici of Cesare Baronio, were erroneous, the scandalous products of ill-intentioned and shoddy research.

The idea behind Simon’s work was that in a court of law, good histories—accurate, learned, well argued—would defeat bad ones.

That hope animated Gottfried Ollearius’s brief on behalf of the theology faculty of Leipzig, which was consulted in a blood libel accusation in 1714. The faculty’s report began by pointing out that the blood libel was unknown in the first 13 centuries after Christ’s birth. Why, if the Jews needed Christian blood for their rituals, had they refrained from seeking it for 1,300 years? The report then went on to confront the historical arguments of the libel’s many advocates, including de Espina and Baronio, to show that they contradicted themselves. Cardinal Lorenzo Ganganelli did something similar in Rome in 1759, when the Holy Office of the Inquisition was consulted about a blood libel accusation in the Polish diocese of Łuck. Ganganelli’s job was complicated by the fact that he undertook his task under Pope Benedict XIV, whose bull Beatus Andreas just four years earlier endorsed the story of another child’s murder, that of Andreas of Rinn, at the hands of the Jews. Ganganelli’s conclusions were mixed: He asserted that the Jews of Poland did not deserve Christian sympathy but allowed that the ritual murder of children was probably not among their crimes.

All of these scholars fought fire with fire, writing histories that pointed out the interpretive errors and manipulations of the accusers. But the hope that good history would drive out bad history was almost always disappointed: None of these scholarly reports did much to lessen the power of the blood libel against Jews. Perhaps that is in part because, as Teter notes, they were not widely distributed. Simon’s work appeared in a very limited edition. The Leipzig brief went unprinted for 40 years. Ganganelli’s report was buried in the Vatican archives until the 20th century.

Would things be different if these historical inquiries into the blood libel had circulated more broadly? Lord Nathaniel Rothschild certainly thought so. When Mendel Beilis, a Jew of Kiev, was accused of killing a 13-year-old Christian boy in 1911, Rothschild wrote to the Vatican’s secretary of state, Cardinal Rafael Merry del Val, asking him to confirm the existence of Innocent IV’s medieval absolution of the Jews and of the Ganganelli report, two documents he thought would make clear to Christians the falsity of the accusations. (The cardinal responded by certifying the existence of both documents.) The great Jewish historian Cecil Roth did something similar in 1935, when he responded to Der Stürmer’s ritual murder issue by publishing Rothschild’s correspondence with the Vatican, including a photograph of the envelope in which the Vatican had sent its response, lest anyone doubt its authenticity.

I am not as optimistic as Roth, Rothschild, and presumably Teter that the availability of better, truer histories of the blood libel can defeat this vicious myth. Such works—I’ll call them forensic histories—are certainly important, but they are also clearly insufficient. The forensic historian engages in a critical reexamination of the evidence in the hope of reversing a historical injustice, much as the researchers of the Innocence Project today might bring new proof to a court of law in order to overturn a wrongful conviction. Teter’s book assumes a well-deserved place in this illustrious tradition of forensic history on the blood libel, and we should all be grateful for it, since the task remains vitally necessary.

But if pointing out to the libel’s purveyors that their forensics and history are wrong were enough to defeat it, there would be no blood libel today. Already in 1475, when Jews in Trent were arrested on the grounds that Simon’s body bled when they were in its presence, many doctors knew better than to accept the prosecutor’s argument that “experience shows that wounds on the dead emit blood when a murderer stands near the corpse.” They also knew better in 1747, 1753, and 1766, when the same bleeding-corpse argument was used to accuse Jews of ritual murder in Poland.

The limitations of forensic history are not only that it doesn’t circulate as widely as the libels it seeks to counter. It also says too little about why certain ideas about Jews and other marginalized groups have proved so resonant in particular times and places, so capable of promoting violence, and so foundational to the exclusions and inclusions that societies have come to regard as necessary. To reverse wrongful convictions past and present, therefore, it’s just as important to bring to light the structural conditions that nourish and are nourished by those injustices.

The Italian historian Carlo Ginzburg once suggested that conspiracy theories about how Jews and other marginalized groups were scheming to destroy society—accusations like the blood libel and the witches’ Sabbath—were the product of a fundamental shift in European mentalities and myths that took place amid the famines, plagues, and wars of the 14th century. If that is true, then our structural question only becomes more pressing. Why have these ways of thinking about the world proved so persistent and so capable of dissemination across historical periods and cultures, even into our own era? Regardless of the historical context in which they may have originated, what has given logics of conspiracy the ability to draw renewed life from the technologies, disciplines, and communications techniques of every subsequent age, including our own? For it is all too clear that the trail that Blood Libel set out to follow has not yet come to an end.

Today’s conspiratorial myths, such as the replacement theory—the idea that Jews seek to destroy white, Christian Europe and the United States by promoting immigration, integration, and civil rights—come shrouded like their predecessors in arguments drawn from disciplines like history, psychology, and biology, disseminated now not only by the printing press but also by the latest in algorithms and bots. As I write, Facebook is working to remove posts blaming the spread of the coronavirus on Jews.

Why are such myths so persistent? What makes them so appealing and therefore so useful? Forensic histories may help us reverse wrongful convictions, but they can’t answer these structural questions. We need histories that teach us how our societies learned to imagine themselves (as they still too often do) as threatened by the malevolent conspiracies of the marginalized. Then we could begin the critical work of unlearning them.